"Rupert Murdoch is a megalomaniac twister, surrounded by yes-men and hatchet-men". That sharp description by Hugh Trevor-Roper was contained in a February 1982 letter to his confidant, the historian Blair Worden.

It is just one of the critical references to the News Corporation chief that are revealed for the first time in a just-published biography of Trevor-Roper*.

Trevor-Roper was appointed as a national director of Times Newspapers in 1974, seven years before Murdoch lobbied to acquire The Times and Sunday Times.

By the time, in 1981, when Murdoch emerged as the favoured bidder Trevor-Roper had acquired a life peerage, becoming Lord Dacre of Glanton. He was one of the four directors who extracted promises from Murdoch designed to protect the editors of the titles.

But Murdoch's first act was to add two of his own nominees to the board of directors, weakening its independence. Dacre's first clash came when he "expressed reservations" about the switching of the Sunday Times editor Harry Evans to the editorship of The Times.

Dacre came to distrust Murdoch's taste and his motives, as he revealed in a Daily Telegraph interview published just after his death in 2003, and a passage is reproduced in the book:

I felt that whatever he [Murdoch] touched went down-market, though it also moved from loss into profit. For the sake of sales, he aims to moronise and Americanise the population.

He also wants to destroy our institutions, to rot them with a daily corrosive acid... He certainly has a hatred of what he considers the stuffiness of the British establishment.

He tends to put peers on his board, and they're not useless peers either, but I think he's saying, 'All these people are buyable, they're digging their own graves for me".

Dacre's second clash with Murdoch followed the transfer of the ownership of the newspaper titles from a separate company into News International. It was that which prompted Dacre's "megalomaniac" remark.

In the event, the transfer was cancelled but Dacre had no illusions that the national directors would be able to restrain Murdoch in the long term. In another letter to Worden, Dacre wrote:

I know perfectly well that it can't last. Whatever we think, we are courtiers in an oriental Sultanate, and there is a corps of janissaries, with bowstrings at the ready, at the palace door.

Dacre was still in place as a director in 1983 when the episode that was to bedevil the rest of his life occurred - the saga of the fake Hitler diaries. The man widely respected for his scholarship on Hitler was to jeopardise his reputation by initially authenticating the fakes and then changing his mind too late to prevent publication.

The book devotes several pages to explaining Dacre's role. There is little in the account that is new, including the fateful moment when Dacre reached The Times's deputy editor, Colin Webb, to say he was no longer satisfied the diaries were genuine.

By then, the paper had announced in print that the Sunday Times would be publishing the first instalment of its serialisation the following day. But a breakdown in communications meant that no-one thought to tell the Sunday Times's editor, Frank Giles.

So the story appeared with a statement that Dacre had "staked his academic reputation" by endorsing the diaries. When Dacre finally admitted his doubts to Giles, the editor called Murdoch to ask whether he should stop the presses.

As is well known, Murdoch replied: "Fuck Dacre. Publish."

Altogether less well known is the devastating effect on Dacre after the forgery was subsequently exposed. His academic enemies rounded on him, rival papers ran highly critical pieces and he suffered from a great deal of private abuse.

As Master of Peterhouse, he was not universally admired and a humiliating limerick began to circulate in Cambridge:

There once was a fellow called Dacre,Who was God in his own little acre,But in the matter of diaries,He was quite ultra vires,And unable to spot an old faker.

That was mild in comparison to some very hostile letters he received. The biography notes:

The damage to his reputation was substantial and long-lasting. For him, if not for Times Newspapers, the Hitler diaries proved a disaster.

But Dacre stayed on as a director, crossing the picket lines in 1986 after Murdoch ousted the print unions to publish the papers from Wapping and expressing his admiration for the move.

Months later, he and his fellow directors protested at the publication of a Sunday Times front page story, "Queen dismayed by 'uncaring' Thatcher", which claimed there was a rift between monarch and prime minister. One director broke ranks, Murdoch played his hand cleverly and the rebellion passed.

The following year Murdoch asked Dacre to step down as a director. He protested and, according to the book, "Murdoch showed he was not pleased by this resistance." It was followed by a visit to Dacre by Murdoch's lawyer - and, "having made his gesture of defiance" - Dacre resigned.